Device for bracing a shell in an aircraft fuselage

ABSTRACT

A device for bracing a shell surface in an aircraft fuselage against deformations and consisting of a continuous profile that is arranged so as, after conformation, to be mounted against the shell surface. Notches are spaced at regular distances apart from each other in at least a portion of the profile. The notches extend through a base surface in the profile, and through an intermediate part perpendicular to the base surface. The notches are delimited upwardly by an upper surface that is not encompassed by the notches.

TECHNICAL AREA

This invention concerns a device for bracing a shell surface in anaircraft fuselage against deformations and consisting of a continuousprofile that is arranged so as, after conformation, to be mountedagainst the shell surface.

STATE OF THE ART

All types of aircraft are subject to heavy stresses. Nevertheless,production methods must be simple in order to keep costs at acceptablelevels. These somewhat contradictory criteria are particularlyapplicable in connection with the fabrication of curved surface sectionsor panel surfaces used for the fuselage, wings or other parts of theaircraft.

Practically all outer surfaces of modern aircraft, be they military orcivilian, are braced by means of one or more of the following methods:

-   -   Frame ribs    -   Stringers    -   Cell layers (honeycomb sandwich)

A stringer is often used in thin-sheet structures to brace a shellsurface against deformations perpendicular to the sheet surface. Panelsor outer sections with an outer surface part in the aircraft areequipped with supporting ribs. When these supporting ribs are disposedlongitudinally, the term “stringer” is used. The purpose of thesesupporting ribs is to divide the aircraft surfaces into an optimalconfiguration so as to counteract deformation of the fields between thestringers.

Areas where there is a need for curved stringers on aircraft include:

-   -   Front and rear cabin body    -   Leading edges of the wings    -   Stabilizer panels    -   Double-curved openings    -   Control surfaces

One problem with using stringers is that it is very expensive to producestringers whose geometry conforms to the location in the aircraft wherethe element is to be used. When the surface of the fuselage is curved itis necessary to either mill or stretch the stringer into the desiredshape, which is very expensive.

DESCRIPTION OF THE INVENTION

The foregoing problem is described by means of a new stringer design. Inthe design according to the invention a continuous profile of, e.g.light metal is used as a stringer. Notches are made at a regulardistance apart from each other in at least a portion of the profile. Thenotches extend through a base surface in the profile and through anintermediate part in the direction perpendicular to the base surface.The profile also contains an upper surface that is parallel to said basesurface, which upper surface is not encompassed by said notches.

When the stringer according to the invention is being mounted againstthe shell surface, it can be easily bent and conformed to the shape ofthe shell surface. After mounting, the stringer and the shell surfacetogether form a strong and rigid unit.

One advantage of the solution according to the invention is that boththe stringer and the shell surface are soft and workable prior to theirbeing assembled together, while the finished assembled structure isstrong and stable. The workable stringer radically affects durabilityand strength vis-a-vis loads that are perpendicular to a sheet surface,while the costs of conforming the stringer can at the same time be keptat a very low level.

BRIEF DESCRIPTION OF FIGURES

FIG. 1 Perspective view of mounted stringer

FIG. 2 Side view of mounted stringer

FIGS. 2 a–2 b Sectional view of a mounted stringer

FIGS. 3 a–3 d View in cross-section of various possible profile designs

DESCRIPTION OF EMBODIMENTS

A stringer 2 can consist of a continuous profile of workable material,such as an extruded aluminum profile. FIGS. 3 a–3 d show a number ofpossible cross-sections for such a profile. The cross-section consistsof a base 3 and an intermediate part 4 oriented perpendicular thereto,plus an upper surface parallel to the base 3. Designs involving a base3, an intermediate part 4 and an upper surface 5 other than those shownin the figures are also possible. A typical thickness d for the walls ofthe profile is roughly 1–2 mm. The thickness of the base, theintermediate part and the upper surface may differ.

The stringer 2 must be conformed for mounting against a curved shellsurface 1 in an aircraft fuselage. To facilitate this conformation,notches 6 are made at predetermined distances apart from each otheralong the length of the profile. In a preferred embodiment these notches6 are spaced at a regular distance a apart from each other in order tothereby render the stringer structure independent of the shape of theaircraft section in which the structure is to be used. An appropriatedistance between the notches can be roughly 25 mm, but this distance isof course dependent on the shell surface against which the stringer isto be mounted. It is also possible to make notches with varyingdistances between them along different portions of the length of theprofile. The notches can extend through the base surface 3 and theintermediate part 4 in the direction perpendicular to the base surface3. The notches are delimited upwardly by the upper surface 5, which thusis not encompassed by said notches 6. The base surface 3 and the uppersurface 5 are joined via said intermediate part and realized in onepiece therewith. The notches can be, e.g. milled or cut from theoriginal profile. Stringers with notches can also be fabricated as yardgoods, i.e. at low cost.

As a result of the design solution according to the invention, thestringer 2 can be easily bent and conformed to the shell surface 1 forthe part of the fuselage against which the stringer is to be mounted.FIG. 1 shows a perspective view of two stringers 2 mounted against ashell surface 1.

Mounting can be accomplished by various methods, such as riveting,bolting, welding or gluing. Once the stringer is mounted against theshell surface, the frame ribs can be secured in the usual way.

1. A device for bracing a shell surface in an aircraft fuselage againstdeformations and comprising a continuous profile that is arranged so as,after conformation, to be mounted against the shell surface, said devicecomprising: at least one base surface that is arranged so as to lieagainst the shell surface; at least one upper part parallel to said atleast one base surface, said at least one upper part having asubstantially rectangular cross-section; and said at least oneperpendicular intermediate part connecting the base surface and at leastone upper part, wherein the profile has notches along at least a portionof the length of the profile spaced at a regular distance from eachother, which notches extend at least through the at least one basesurface and through the entirety of the at least one intermediate part,and wherein the notches are delimited upwardly by said at the least oneupper part, which at least one upper part is not encompassed by saidnotches.
 2. A device according to claim 1, wherein the base surface isarranged so as to be fastened to the shell surface.